This invention relates generally to a method of forming a built-up film of a J-aggregated organic dye and, more specifically, to a method of treating a built-up film of an organic dye with a magnetic field to cause the organic dye molecules to be aggregated in the J-state or to promote the formation of such J-aggregate.
There is known a technique in which a plurality of monomolecular films of an organic dye each developed on the surface of water are built up on a substrate. Such a built-up film having a two-dimensional structure is called "Langmuir-Blodgett's film" (hereinafter referred to simply as LB film for brevity). LB films are useful in application for optically functional materials such as photoelectric transfer elements, optical recording materials, non-linear optical elements or display elements (H. Nakahara, Journal of the Japan Oil Chemist's Society 34, 774-783 (1985)).
Among such LB films, those of a type in which the organic dye molecules are aggregated or associated in the J-state draw a particular attention because the J-aggregated organic dye shows peculiar visible light absorption characteristics, i.e. the absorption band is shifted to a longer wavelength and has a smaller half band width in comparison with the organic dye in the non-aggregated, monomeric state and because the J-aggregated organic dye gives higher photoelectric transfer efficiency and higher luminous efficiency. Thus, LB films of the J-aggregated dye may be also used for irreversible memory and reloadable memory applications.
The term "J-aggregated state" or "J-aggregation" is defined as an aggregation state of dye molecules in which bathochromic shift of the first electronic transition of the dye occurs. For details reference should be made to E. Daltrozzo et al, Photogra. Sci. & Eng. 18, 441 (1974).
One known method for forming or promoting the formation of J-aggregated dye films includes incorporating a long chain hydrocarbon or a long chain fatty acid ester into a dye-containing composition from which monomolecular films are to be prepared. Also known are a method in which LB films are exposed to an atmosphere of ammonia gas, a method in which LB films are exposed to humid conditions and a method in which LB films are exposed to a light or heat. These methods, however, are not advantageous because there is a danger of deterioration of the LB films.